The conversion of organic acids and alcohols to corresponding organic esters for industrial applications has been widely studied. Organic esters are used in a wide variety of applications, including the areas of biofuels, food flavors and fragrances, and solvents.
Fermentation processes using microorganisms provide a promising path for converting biomass and agricultural wastes into chemicals and fuels. There are abundant low-value agricultural commodities and food processing byproducts or wastes that require proper disposal to avoid pollution problems. In the dairy industry, approximately 80 billion pounds of cheese whey byproduct are generated annually, much of which has no economical use and requires costly disposal. Similarly, in the corn refinery industry, more than 22% of the estimated 12 billion bushels (approximately 300 million metric tons) of corn annually produced in the United States is processed to produce high-fructose-corn-syrup, dextrose, starch, and fuel alcohol. It is thus desirable to convert these byproducts and wastes to high-value products to reduce waste while improving the process economics.
Bioethanol is the major biofuel currently available on the market. Recently, however, biobutanol has attracted attention for its potential as a transportation fuel because biobutanol is noncorrosive and offers a safer fuel that can be dispersed through existing pipelines and filling stations. As a biofuel, butanol has the following advantages over ethanol: (a) butanol has 30% more Btu per gallon; (b) butanol is less evaporative/explosive with a Reid vapor pressure (RVP) 7.5 times lower than ethanol; (c) butanol is safer than ethanol because of its higher flash point and lower vapor pressure; and (d) butanol is more miscible with gasoline and diesel fuel but less miscible with water.
Butyrate esters have similar energy content and properties to biobutanol but offer the advantage of being easier to produce than biobutanol. More specifically, butyrate esters have similar energy content to butanol, are substantially insoluble in water, and have lower vapor pressures and higher flash points than ethanol. Butyrate esters may be produced from sugars via butyric acid fermentation followed by esterification with an alcohol. Thus, butyrate esters offer a novel alternative to existing biofuels.
Short-chain organic acid esters are also widely used as flavor and fragrance compounds in food, beverage, cosmetic, and pharmaceutical industries. Currently, most of the flavor compounds are provided by traditional methods such as chemical synthesis or extraction from natural sources. As a result, additional embodiments for methods and processes for producing esters are desired.